Beach Processes, Berrien County, Michigan

Abstract

The level of Lake Michigan rose both markedly and rapidly in the decade 1964-1974. Theoretically, a significant rise in lake level should be accompanied and followed by an important increase in beach erosion; much or most of the sand eroded should be carried offshore, rather than in the littoral drift system. Computer simulation, measures of erosion rates on air photos, depletion of an artificial sand stock-pile, beach pad histories and other studies indicate that the theoretical effects have also been the actual results. The theoretical projection is confirmed. The importance of transverse transport (more or less at right angles to littoral transport) in the study area points up the fact that presentlyknown types of coastal defense works, largely designed with littoral drift in mind, may not be effective on segments of coast where water levels are rising, or have recently risen significantly. Although littoral drift in the study area has been limited, it has operated clearly in the form of “beach pads”, discrete masses of sand which move at measurable rates. Beach pads were derived from an artificial stockpile of sand, but in this case not from erosion of the natural dunes. Each beach pad, with its associated bar, furnishes a diagonal path along which sand is transported from the beach into deeper water, under oblique wave attack. The amount of sand moved offshore in this way is not measured by considering the migration rate of the pads.